1. Field of the Invention
The present invention relates to the use of cellobiohydrolase from Phanerochaete for the utilization of a biomass such as cellulose.
2. Description of the Related Art
In recent years, biomass created by the photosynthetic action of plants has shown increasing promise as an alternative to finite petroleum resources. Among these, the utilization of cellulose shows great promise. Cellulose is a polymer in which the sugar glucose is condensed via β-1,4 linkages, and it has a strong crystalline structure due to intermolecular hydrogen bonding. At least three types of cellulose degrading enzymes (cellulases) are required for the efficient degradation (saccharification) of cellulose to a monosaccharide, and it is thought that degradation only becomes possible through the cooperative action thereof (Hereinafter, this effect is referred to as a synergistic effect). These three types of cellulases are an exo-form (cleaving disaccharide units from the ends) cellobiohydrolase (CBH), and an endo-form (randomly cleaving) endoglucanase (EG) that both act directly on the cellulose polymer, and a β-glucosidase (BGL) that acts on oligomers of various sizes produced by these enzymes and breaks them down into monosaccharides.
Degradation of the polymer structure comprising crystalline cellulose presents great difficulties. There is a strong need for enzymes that can fully decompose such a structure, as well as for a combination thereof having a synergistic effect on cellulose degradation.
In light of this situation, combinations of different types of cellulases that can act most synergistically and decompose cellulose efficiently is being widely investigated. For example, it is known that one of the aforementioned three types of enzymes, cellobiohydrolase (CBH), comprises CBHI, a member of glycoside hydrolase family (GHF) 7 that cleaves from the reducing end of the cellulose chain, and CBHII, which is a member of GHF6 and cleaves from the non-reducing end. There have been various published reports concerning cellobiohydrolase. For example, it has been reported that among the forms of cellobiohydrolase produced by Phanerochaete chrysosporium (Pc), which belongs to the genus Phanerochaete, CBHI has a greater synergistic effect on cellulose degradation than CBHII when it is combined with a different type of cellulase. More specifically, a combination of CBHI produced by Pc and CBHI produced by an organism other than Pc was found to be superior to a combination of CBHI produced by Pc and CBHII produced by Pc (Uzcatsgui et al, J. Biotechnol. 19(2-3):271-85). Furthermore, a combination of CBHI produced by Pc (PcCBHI) and EG produced by Pc (PcEG) being superior to a combination of CBHII produced by Pc (PcCBHII) and EG produced by Pc (PcEG) has also been reported (Uzcatsgui et al, J. Biotechnol. 21(1-2):143-59).
It has also been reported that in the case of Trichoderma reesei, which belongs to the genus Trichoderma, the synergistic effect of CBHI on cellulose degradation is greater than that of CBHII when it is combined with a different type of cellulase. For example, it has been reported that a combination of PcEG III and TrCBHI is superior to a combination of PcEG III and TrCBHII (Henriksson et al, Eur. J. Biochem. 259 (1-2):88-95).